Hey Woodsey,
Have a look on redbook.com, they list all the different types of series codes & a lot of it means that they are either petrol/diesel, turbo or natural. Also weather it is a cab chassis (ie. tray back) or utility (ie. well body) I have a KZN165R MY02 which is a 2004 Turbo Diesel tray back & in 2004 they came out with a model in January & also another model in June which is the MY04.
I also did a lot of searching on carsales, carguide, drive, ebay & all those sights that sell cars. After a while you will notice the difference in the series codes & what they mean.
Hope this helps,
Jason